Nandan Kumar Sinha

The prime focus of this work is to estimate stability and control derivatives of an airship in a completely nonlinear environment. A complete six degrees of freedom airship model has its aerodynamic model as nonlinear functions of angle of attack. Estimating the parameters of aerodynamic model in a nonlinear environment is challenging as it demands an exhaustive dataset that could cover the entire regime of operation of airship. In this work, data generation is achieved by simulating the mathematical model of airship for different trim conditions obtained from continuation analysis. The mathematical model is simulated using predicted parameter values obtained using DATCOM methodology. A modular neural network is then trained using back-propagation and Adam optimisation algorithm for each of the aerodynamic coefficients separately. The estimated nonlinear airship parameters are found to be consistent with the DATCOM parameter values which were used for open-loop simulation. This validates the proposed methodology and could be extended to estimate airship parameters from real flight data.

A sliding-mode (SM) controller designed for recovery of an aircraft from flat oscillatory spin is discussed. Aircraft controls aileron δa, rudder δr, and elevator δe were used as active controls within the limits. A sliding surface was designed depending upon available control authority and acceptable error dynamics. SM controller based on variable-structure control technique for nonlinear systems is suitable for all nonlinear controllers. Limits on the control surfaces, both in position and in rate, are maintained during the computation of control commands. The low-angle-of-attack segment is the stable level-trim state. The SM controller recovers the aircraft to the level flight trim state within the limits specified on the rudder saturation rates, which could be achieved using the nonlinear dynamic inversion (NDI) controller.

The short take-off capability is of paramount importance for a fighter airplane to enable its operation from short and damaged runways. This paper analyses the airplane take-off process from the viewpoint of reducing the ground roll/take-off distance with the use of thrust vectoring. The airplane take-off is modelled incorporating the ground reactions on the landing gear and the thrust vector forces and moments. The take-off problem is formulated as an optimal control problem with appropriate constraints. Though many researchers have applied optimal control techniques for designing airplane manoeuvres, its application to the airplane take-off problem is rarely available in the open literature. It is expedient to use such methodology to understand the use of thrust vectoring features of an aircraft to maximise the benefits in shortening the ground roll/take-off distance. An optimal control methodology has been applied in this paper with the objectives stated above to a twin-engine fighter nonlinear aircraft model popularly known as F-18/HARV. Computation of flight path and control schedules using optimal control has been carried out with and without the use of vector nozzles. A reduction of about 6% in take-off distance and about 29% in ground roll distance is obtained with the use of thrust vector for the configuration studied.

Being a high throughput technique, enormous amounts of microarray data has been generated and there arises a need for more efficient techniques of analysis, in terms of speed and accuracy. Finding the differentially expressed genes based on just fold change and p-value might not extract all the vital biological signals that occur at a lower gene expression level. Besides this, numerous mathematical models have been generated to predict the clinical outcome from microarray data, while very few, if not none, aim at predicting the vital genes that are important in a disease progression. Such models help a basic researcher narrow down and concentrate on a promising set of genes which leads to the discovery of gene-based therapies. In this article, as a first objective, we have used the lesser known and used Singular Value Decomposition (SVD) technique to build a microarray data analysis tool that works with gene expression patterns and intrinsic structure of the data in an unsupervised manner. We have re-analysed a microarray data over the clinical course of Septic shock from Cazalis et al. (2014) and have shown that our proposed analysis provides additional information compared to the conventional method. As a second objective, we developed a novel mathematical model that predicts a set of vital genes in the disease progression that works by generating samples in the continuum between health and disease, using a simple normal-distribution-based random number generator. We also verify that most of the predicted genes are indeed related to septic shock.

Tools based on the bifurcation and continuation method have been found to be extremely useful for studying multiparameter nonlinear dynamical systems under state and parameter-constrained conditions. Because of inherent limitations of the existing methodologies, however, application of continuation techniques to certain types of problems has remained cumbersome and even computationally challenging. This paper provides an alternate direct approach in MATLAB® using its continuation subroutine MATCONT to extend the capabilities of continuation techniques in an attempt to accommodate a wide variety of constrained dynamics problems. Published results in the literature are first reproduced for validation of the proposed approach. A control problem of scheduling gains for the longitudinal flight dynamics of an aircraft is next presented to show usefulness of the proposed methodology, followed by solutions to an aircraft conceptual design problem involving wing morphing with eigenvalue constraints, with the difficulties of the selected problems increasing in that order.

Thrust vector nozzles are finding place on modern fighter airplanes because of the benefits they provide and also due to diminishing weight penalty of such nozzles. They offer additional benefits in the case of a twin-engine airplane. Different vectoring configurations such as multi-axis vectoring, single-axis pitch vectoring and single-axis vectoring with canted nozzles have been studied with respect to twin-engine airplane configuration. Modeling and integration of thrust vector nozzles with rigid airplane six-degrees-of-freedom equations of motion have been carried out in this article. Using the integrated model, a comparative study is carried out to summarize the capabilities and limitations of various nozzle configurations with respect to performance of an airplane in velocity vector roll and in Herbst maneuvers. The airplane model used in this work is the F-18/HARV and all simulation results have been produced using a nonlinear dynamic inversion controller developed in Matlab/Simulink environment. Results show that a multi-axis thrust vectoring provides additional benefits as compared to single-axis vectoring with canted nozzles in high angle of attack velocity vector roll and in Herbst maneuvers. The single-axis pitch only vectoring has roll control power and lacks in yaw control power, to execute the velocity vector roll maneuver. © IMechE 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

Aircraft dynamics are dominated by nonlinearities that may drive the aircraft into chaotic motions under certain conditions. Past studies in this area have explored several factors leading to the evolution of chaotic dynamics. However, a proper route or sequence for the evolution of chaotic dynamics has not been adequately substantiated. In this context, this paper systematically examines possible routes to chaos in the post-stall dynamics of an F-18 High-Alpha Research Vehicle model with external steady wind as the driving agent. Using tools from nonlinear dynamics based on bifurcation analysis, phase portrait, Poincaré map and amplitude spectrum analysis techniques, existence of quasi-periodic, period-doubling and intermittency routes to chaos are established. An eighth-order nonlinear aircraft model incorporating wind effects has been used for generating time responses from different post-stall flight conditions.

Design of maneuvers for carefree access of an aircraft to its complete flight envelope including poststall regimes is useful not only from a combat strategy point of view, but also for devising recovery strategies from an accident scenario. Maneuvers for an aircraft can be efficiently designed if a priori knowledge of its maneuverability characteristics is available to the control designers. Different types of agility metrics that characterize aircraft maneuvering capabilities have been proposed in literature based on different criteria. The concept is based on the assumption that the boundary of the AER is defined by saturation of one or more control surfaces. Therefore, a point lying on the boundary of AER is initially located using a continuation method. Using the trim point on the boundary as a starting condition, a separate continuation procedure is carried out, with the saturated control fixed at its limit value to obtain the envelope containing attainable equilibrium points.

Illustrative examples are presented in this paper to show the applications of the continuation-algorithm-based, recently developed extended bifurcation analysis (EBA) methodology to compute optimum flight parameters of an F/A-18 high-angle-of-attack research vehicle aerodynamic model. A complete model describing the six-degree-of-freedom motion of aircraft is used in this analysis to compute trims for the aircraft in constrained flights, for example, straight and level and steady climb flights. Using the results of such computations, one can plot the performance curves for aircraft which are in contrast to the performance curves usually available in the aircraft design text books. Special features of the performance curves computed here are high-lighted and the reasons for the contrasting features between the performance curves obtained here and the corresponding ones presented in the aircraft design text books are discussed. Primary objective of this work is to show the efficiency of the EBA methodology in evaluating the optimum values of multiple objective functions which usually requires the use of the optimization theory-based numerical techniques and can be generally computationally exhaustive in terms of time and efforts. © IMechE 2007.

Deploying flare decoys against heat-seeking threats involves various parameters such as flare timing, flare ejection velocity, direction of ejection and the number of flares used. In this study, an attempt has been made to identify the key parameters among these that impact the performance of flares the most. For this, engagement studies involving sixdegrees- of-freedom models for an air-to-air heat-seeking missile and a fighter aircraft were carried out using the CADAC++ simulation environment. The effect of flare parameters was studied using their impact on missile envelopes. Studies show that the effectiveness of the flare decoys is a strong function of the flare timing and the number of flares used.